Various types of devices may require hermetic sealing to protect the active components from atmospheric elements, such as moisture and/or gases. For example, devices which include organic active elements such as OLEDs require protection from moisture or gases. OLED devices can serve as displays for various types of consumer electronic products, such as automobile stereo displays, cellular phones, cellular smart phones, personal organizers, pagers, advertising panels, touch screen displays, teleconferencing and multimedia products, virtual reality products and display kiosks.
Referring to FIG. 1, a conventional OLED device is shown. The OLED device comprises a functional stack formed on a substrate 101. The functional stack comprises one or more organic functional layers 102 between two conductive layers (104 and 106) which serve as electrodes. The conductive layers are patterned to form rows of cathodes in a first direction and columns of anodes in a second direction. OLED cells are located in the active region where the cathodes and anodes overlap. Charge carriers are injected through the cathodes and anodes via bond pads 108 for recombination in the functional organic layers. The recombination of the charge carriers causes the functional layers of the cells to emit visible radiation.
Active components, such as the cathode and organic layers in organic devices are adversely impacted by potentially deleterious components such as water, oxygen and other gaseous components. One approach is to hermetically encapsulate the device with a cap 110, sealing the cells. Typically, an epoxy based sealant 112 is used to bond the cap to the substrate. However, the sealant can be penetrated by potentially deleterious components such as moisture, oxygen and other gases. Small amounts of such deleterious components can be trapped in the encapsulation during the sealing process. Additionally, such deleterious components may diffuse into the encapsulation over time. This can adversely impact the reliability of the OLED device.
To improve the sealing of the encapsulation, a drying agent 114, such as barium oxide, calcium oxide or sodium oxide directly above the active region where the active components are located. However, the penetration path of moisture, oxygen and other gases from the atmosphere is along the interface of the cap and substrate, where the sealant 112 is located. By locating the drying agent away from penetration path, small amounts of water and gases can escape sorption and react with the active components, thus degrading the life expectancy of the organic device.
As evidenced from the foregoing discussion, it is desirable to provide an improved encapsulation to prevent degradation in performance and increase the lifetime of a device.